Telephone system



July 9, 1940. c. E. BEALE ET AL TELEPHONE SYSTEM Filed Sept. 17, 1938 7 Sheets-Sheet 1 INVENTORS MUND 8 CHARLES ED ERLE IDRIS TREVOR RICHARDS owen AVIS PEARCE ATTORNEY;

July 9, 1940. c. E. BEALE ET AL TELEPHONE SYSTEM Filed Sept. 17, 1938 7 Sheets-Sheet 2 mvsnrons CHARLES EDMUND BEALE loans maven mcmnos OWEN RVIS PEARCE Z ATTORME? July .9, 1940. c. E. BEALE ET AL TELEPHONE SYST Filed Sept. 17, 1958 7 Sheets-Sheet 3 INVENTOR '5 a Y R E EMF N BHC R DE m N H T WR A w m R HT L N R5 m m Cm July 9, 19462 c. E. BEA-LE ET AL 2,207,530

TELEPHONE SYSTEM Filed Sept. 17, 1938 7 Sheets-Sheet- 4 mvsuran's CHARLES 50mm: BEALE mms TREVOR RICHARDS BY Z OWEN AVIS PEARCE ATTORNE July 9, 1940. c. E. BEALE ET AL- TELEPHONE SYSTEM Filed Sept. 17, 1938 7 Sheets-Sheet 5 INVENTORS CHARLES ammo BEALE mans maven mcnnnos %o szrwws macs ATTORNE? July 9, 1940. c. BEALE ET AL 2,207,530

TELEPHONE SYSTEM Filed Sept. 17, 1938 7 Sheets-Sheet 6 mvswra'k's CHARLES somuuo BEALE mms TREVOR RICHARDS WEN V! P C BY :0 A s EAR E ATTORNEY July 9, 1940. c. E. BEALE ET AL 2,207,530

' TELEPHONE SYSTEM Filed Sept. 17, 1938 7 Sheets-Sheet 7 INVENTORS CHARLES EDMUND BEALE IDRIS TREVOR RICHRRDS owan AVIS PEARCE Z ATTORNEY Patented July 9, 1940 UNITED STATES.

OFFICE 2,207,530 TELEPHONE SYSTEM Application September 17, 1938, Serial No. 230,416 -In Great Britain October 6, 1937 '20 Claims. (01.179-26) The present invention relates to telephone-systems and is more particularly concerned with the provision of telephoneservice in an area involving a main exchange, a few satellite exchanges, and 51: a number of small exchanges provided with automatic switching equipment controlled from the main exchange which will be referred to hereafter as R. C". X.s. "The invention is mainly concerned with the equipment in the satellite exo' changes and particularly with switches usually known as discriminating selector repeaters which enable economy to be achieved in the-use of junctions and switching equipment for giving the facilities required. The chief object of the inven- 15'1 tion is to provide improved types of discriminating selector repeater which offer special advantages in systems operating on the general principles referred to above.

According to one feature of the invention in a '0:- discriminating selector repeater unit including a hunting switch adapted to select an idle line extending to a main exchange and a numerical switch adapted to extend connections to local switches or adjacent exchanges; impulses trans- 1, mitted over the junction from the main exchange are adapted to effect the setting of the numerical switch. a

According to another feature of the invention in a discriminating selector repeater unit includ- 36-1 ing a hunting switch adapted to 'select an idle line extending to a main exchange and a numerical switch adapted to extend connections to local switches or adjacent exchanges, impulses transmitted over the junction from the main exchange 35 are adapted to be repeated o-ver'the wipers of the numerical switch.

A further feature of the invention is that in a discriminating selector repeater unit including a hunting switch adapted to select an idle line exy tending to a main exchange and a numerical switch adapted to extend connections to local switches or adjacent exchanges, impulses transmitted over. the junction from the main exchange lines.

The invention will be better understood from the following description of examples of its application to a system including a main exchange,

a tandem satellite and a plurality of R. C. X.s one of which is of the tandem type and gives ac- 5 cess to what is described'as a terminal R. C. X. Reference should be had to .the accompanying drawings comprising Figs. 1-7 of which Fig. 1 representsdiagrammatically the general trunk.- ing. layout of the system, while Figs. 2-4 and 5-7 show respectively the circuits of two different varieties of discriminating selector repeater.

, Considering first Fig. l, the subscribers on the main-exchange and the subscribers on the tandem satellite exchanges are provided with dial telephones and are permitted to set up automatically calls to other subscribers on their own exchange. For all external calls the subscribers are instructed to dial a distinctive digit which routes their connection to the manual board at the main exchange where their requirements are attended to by the operator .who connects them automatically with the required subscriber on the external exchange;

The subscribers on the tandem R. C. X.s and the terminal R. C. X.s are not provided with dial telephones and for all calls they must call or ring down to the operator at the manual board in the main exchange who extendsthem automatically to subscribers in their own exchange or to sub 'scribers in a different exchange as required. Generally speaking the main exchange may cater for say 1600-3000 lines, the tandem satellite for say 100-200 lines and the tandem R. C. X. for say 10-50 lines.

The terminal R. C. X. is shown in Fig. 1 as an all-relay board and is assumed to cater for 10 As a special feature of this board since only one link circuit is provided it is arranged that the dialling and ringing equipment are 10- 40 cated in a common group divorcedfrom the link circuit. By this means when the link is in use on a local call it is still possible to complete an incoming trunk call over the free common equipment. The same facilities could of course be provided using 12-point uniselectors connected back to back in place of relays and in point of fact if there waslever any possibility of the terminal R.

C. X. being converted to a tandem R. C. X. at some later date; it would be preferable to use unisearise in connection with the design of the discriminating selector repeaters, hereafter termed D. S. R.s, which are used in the tandem satellite exchange and as will appear from the following description particularly on certain types of call.

For instance in the case of local calls the D. S. R.s will be required to function in the normal manner of performing a rotary hunting operation after the vertical motion and then repeating the in digits forward to set up the local connection. On

up the external connection.

Ei) tant terminal R. C. X. to signal forward to obtain connection with the operator and then if the calling subscriber requires connection to another subscriber on either the tandem or terminal exchange the D. S. R. must be adapted for dialling 2.; back over its own incoming circuit under control kinds of calls as well as others will be better of the operator in order to repeat backwardly thepulses necessary for setting up the local connection.

-, The operation of the system for the above appreciated from the following description of the sequence of operations which take place, reference being had to the trunking diagram Fig. 1. When a subscriber SI on the tandem R. C. X.,

5% TR calls, it will be undertsood that a free bothway junction equipment BE? is selected over a relay chain allotter arrangement whereupona link circuit L, preselected over an allotter LA, causes aline finder LP to hunt for the calling line. At

411i the same time the calling signal is repeated in the form of a pulse of ringing current over the junction and bothway junction equipment BEI to the incoming D. S. R. D! at the tandem satellite exchange and in response to the signal this 45; switch associates itself with a free bothway junction to the main exchange M over its associated junction hunter switch JH3 and the bothway junction equipment 3E3. The signal is thereupon repeated to the manual board terminating 50: the junction so as to bring the operator into the connection and she ascer'tains the required numher from the calling subscriber on the tandem R. C. X. In order to verify the correctness of the number which he gives as his own she then dials 55: back through the incoming D. S. R. switch DI.

Generally speaking, verification is required on all calls from R. C. X.s since otherwise the operator will have to meter solely against information received from the calling party which may or may 60 not be correct.

65! propriate level in the usual manner.

'Reverting now to the operation of the incoming D. S. R. during verification, the operator first of all dials the digit designating the incoming connection so that the wipers are raised to the ap- The switch does not hunt however and in place of this a relay is operated over the vertical bank and wiper and serves to by-pass the bridge circuit in the D. S. R. and enable further digits to be repeated '70: back over the incoming junction to set up the verification connection in the R'. C. X. When this is. done the operator should'encounter a busy signal whereupon she cuts in and asks the subscriber to repeat his number as a check against 75,. the original information.

The setting up of the verification connection at the R. C. X. will have necessitated the operation of the connector half FS of the link L already seized by the subscriber on the origination of the call, and if it is now desired to extend him to a local subscriber on the same exchange the operator must first of all release the connector half of the link and then reset it by dialling on to the subscriber required. This is achieved by extending a high voltage pulse from the manual board via the D. S. R. in the tandem satellite which is received at the R. C. X. on a gas discharge tube and relay in series.

In case there are two R. C. X.s connected in series to the tandem satellite as shown in Fig. 1, it will be necessary to arrange for the tandem R. C. X. to relay the high voltage pulse to the terminal R. C. X., R in the case of a call originated from the latter exchange. Incidentally the wipers of the incoming D. S. R. at the tandem satellite are also reset to normal as a result of this releasing pulse.

If the call is to be completed to a subscriber on the same exchange as the calling party, the operator again dials into the incoming D. S. R., which raises its wipers to the same level as before and operates the relay which completes the bypass dialling circuit to the incoming junction. The operator continues to dial back over the junction to set the connecting link already in use to connect with the wanted subscriber who is thereupon rung. When he answers and the subscribers commence to converse, the operator withdraws from the connection thereby releasing the incoming D. S. R., in the tandem satellite and also the link circuit in any tandem R. C. X., which may have been passed through on the way.

In case the call is intended for a subscriber on the tandem satellite, the operations are the same up to the extension of the high voltage pulse to clear down the verification circuit. The operator now dials the local number of the tandem satellite, whereupon the incoming D. S. R., raises its wipers to a position in which a relay is operated to initiate the hunting operation. The wipers thereupon cut in and select the local train of switches which in Fig. 1 might be connected to any of the levels l--5 and the connection is completed in the usual manner. When this is done and the subscribers are in conversation, the operator withdraws from the connection and the R. C. X., and the tandem satellite are left connected to ether.

In case the call is intended for" a subscriber on another R. C. X. adjacent to the tandem satellite, the operation is the same as described up to the release of the verification connection. The operator then resets the incoming D. S. R. to a level such as 6 upon which the hunting operation is initiated to select a junction to the adjacent R. C. X. Further digits are then dialled to connect with the required subscriber on the adjacent R. C. X. and when the two subscribers are in conversation, the operator clears her connections and the two R. C. X's are left connected together via the tandem satellite exchange while the junction from the latter to the main exchange is released.

In case the call is intended for a subscriber on the main exchange or a subscriber on a satellite accessible thereover, the operation is the same as described up to the release of the verification connection. The operator then takes up the other plug of the cord circuit in use and plugs it into the D. S. R, LD in the previous case.

a jack extending to the local switches (not shown) or into a jack connecting with the required adjacent exchange over the junctions such as J l and J2. Further digits are then dialled to connect with the required subscriber and when the subscribers are in conversation the operator clears out of the connection. All apparatus and junctions taken into use are then retained until the subscribers hang up whereupon the operator is signalled accordingly and withdraws her plugs to bring about release.

. In case a call is originated by an automatic subscriber S2 on the tandem satellite exchange he is connected via a line finder SF! to a local D. S. .R., LD which differs from the incoming D. S. R.s such as D! and D2 in that it is not required to repeat dialled impulses backwardly over its own incoming circuit. If a local subscribers number is dialled, the D. S. R. absorbs the first digit and upon the reception of the second digit raises the wipers to the level accomodating the required group of final selectors over which it hunts to pick up a free final selector. The next'two digits are repeated by the D. S. R. to set the final selector wipers into engagement with the desired subscribers line. Thus local calls proceed in a fully automatic manner and such calls are automatically metered.

If however the subscriber requires a call external to his own exchange he dials a distinctive digit such as 0 which raises the D. S. R. Wipers to the tenth level on which hunting is suppressed but on which the hunting of the associated junction hunter switch JHI is initiated to extend the call to the manual board in the main exchange. When the operator plugs in, the discriminating digit is absorbed by the restoration of the D. S. R. wipers to normal. The operator then takes the request of the calling subscriber and dials back over the junction in order to set up a verification connection via the D. S. R. and final selector, and on receiving the busy signal cuts in on the connection to ask the subscriber to repeat his number. The operator then clears down the D. S. R. and final selector and if connection is required with a subscriber on'an exchange accessible from the tandem satellite she proceeds to reset the D. S. R. which hunts to select a junction leading in the desired direction. Subsequent digits are repeated by the D. S. R. to set up the desired connection. When the two subscribers are connected together, the operator clears down her connections thereby releasing the junction to the main exchange.

If connection is required with a subscriber adjacent to the main exchange, the operator after clearing down the verification connection takes up the other plug of the cord circuit and inserts it in a jack extending to the desired exchange and the call is completed thereover as described.

In case a call is originated by a subscriber S3 on the main exchange and is intended for another subscriber on the main exchange the connection is completed in a fully automatic manner over the line finder SFZ on the lines described in connection with a local call within the tandem satellite exchange except that an ordinary first selector S is taken into use in place of If however the subscriber requires a call external to his exchange he dials a distinctive digit for instance 0 and over the corresponding level of the first selector S obtains connection with the operator on the manual board. The operator receives his request and after verification of his number extends his connection over the other plug of the cord circuit in the desired direction. Should he require connection with a subscriber on the tandem satellite exchange TS, the operator will plug into one of the bothway junctions leading by way of the both-way junction equipment BE3 to the incoming selector repeater SR at the tandem satellite exchange. Over this switch she is able to obtain access to the local train of switches in order to set up the desired connection. Alternatively if connection is required with one of the R. C. X.s via the tandem satellite exchange, the incoming selector repeater wipers will be raised to an upper level over which access is had to outgoing junctions leading in the desired direction.

As regards the tandem R. C. X., TR, it should be mentioned that in addition to the arrangements for giving access to ordinary subscribers lines and outgoing junctions provision is also made for connection with Ill-party line equipments constructed aldng the lines disclosed in the application of Owen Avis Pearce filed May 20, 1937, Serial No. 143,653. One set of bank contacts only is allocated to each partly line of this type and connect with what is termed a lO-party line equipment PL adapted to control the setting of the selecting mechanism PI located adjacent to each of the subscribers instruments. In these circumstances the link circuit at the tandem R. C. X. is adapted to perform a repeating function after connection with the desired party linein order to pass on the additional train of impulses required for setting the mechanisms PT.

In the case of revertive calls on a l0-party line circuit, the connection is verified and set up under the control of the operator at the manual board and when the two subscribers are connected together for conversation, the operatorclears out of the connection leaving the party line tied to the link circuit for battery feed and supervision purposes.

Circuits typical of the two types of D. S. R. switches required in the tandem exchange are shown in Figs. 2-7 of the drawings. Figs. 2, 3 and 4 when arranged side by side show the circuit connections of a D. S. R. switch such as DI or D2 in Fig. 1 suitable for terminating a bothway junction from a tandem R. C. X. while Figs. 5, 6 and '7 when arranged side by side show a D. S. R. switch such as LD in Fig. l for use by subscribers local to the tandem satellite exchange. The mechanical construction of both the switches considered is that they are of the vertical and rotary type arranged to have socalled rectangular movement, that is to say, release takes place by further operation of the rotary magnet to advance the wipers clear of the bank after which they fall to the normal level and rotate .back home beneath the bank. A switch of this type is disclosed in the application of Robert Norman Saxby, Patent No. 2,028,689, granted January 21, 1936. The junction hunter switches employed are of the well-known unidirectional rotary type with reverse drive.

Considering now the operation of the incoming D. S. R of Figs. 2-4, it will be understood that the leads I and +l connect with an R. C. X., bothway junction and leads -2, +2 and P2 extend from the D. S. R., bank multiple in the tandem satellite exchange for the purpose of outgoing calls to an R. C. X., the relays IC and OG and their associated contacts constituting a bothway switching equipment such as BEI inFig. 1.

Leads -3 and +3 connect with a bothway junction to the main exchange, and leads 4, +4 and P4 with an incoming selector repeater at the 5" tandem satellite exchange, the relays JA and JB constituting a bothway equipment such as 3E3 in Fig. l.

A call incoming from an R. C. X., subscriber is received as a pulse of earthed ringing current over the incomingjunction lead l and operates relayR over its lower winding which is connected to earth via condenser QE and shunted by rectifier MRA so as to be efliciently responsive to alternating current. Relay R thereupon at armature rl operates relay B and looks over its upper winding while at armature r2 it polarises the shunt field relay D! which is inoperative at this stage. Relay B at armature b2 operates relay which at armature z'c! applies guard earth to the junction test lead 2i? P2 in the D. S. switchmultiple so as to mark the junction as busy. At armature M, Fig. 4, a circuit is completed for relay RC which thereupon at armatures 1-02 and 1-03 connects relay K and the junction hunter switch driving magnet 251 JI-IM to the test wiper II-I4. If the wipers of this switch connect in position I with an engaged main exchange junction, wiper JH4 will encounter earth either over armatures y'a l and i171 if it is engaged by an incoming call received over the junction or by way of the low resistance winding of a KA relay in another D. S. R., in the case of engagement on an outgoing call. Relay K will therefore be shunted and prevented from operating while an energising circuit will be completed for the magnet JHM by way of the magnet interrupter contacts jhm. The magnet on energising disconnects its own circuit and since the switch is of the reverse drive type the magnet on releasing its armature advances the wipers to the 4m next position. This self-interrupted driving action continues until wiper JI-I4 encounters a free outlet which is marked by battery potential by way of the winding of relay JA whereupon relay K will operate in series with the magnet 45 JHM and relay JA in parallel. Due to the high resistance of relay K neither relay JA nor the magnet can operate in series therewith.

Relay K on operating, at armature k4 disconnects relay RC which commences to release slowwily due to its slug, and at armature k6 connects relay KA to the test wiper J H4. Relay KA being of low resistance provides a busying earth potential on the outlet seized, while this relay and relay JA operate in series. Relay JA at armatures ml 551 and m2 connects the main exchange junction leads to the banks of the junction hunter instead of to the incoming selector repeater and at armature dad operates relay JB in readiness for the subsequent release of the junction and busies 00 the junction in the selector repeater banks. During the release time of relay RC an earthed ringing generator is connected over common lead H and armatures lead and rcl to the main exchange junction negative lead 3 so as to signal the op- 65= erator at the manual board. On the release of relay RC the ringing is disconnected from the junction and relays A0 and 0C are connected thereto over normal armatures of relays SY and RR and operated armatures of relays KA and K 70 f in readiness for the reply of the operator.

In case all the main exchange junctions should prove busy, the junction hunter switch will rotate to the last position. This position is not wired to a junction and is not multiplied to other switches 75 3 so that the test wiper JH4 will encounter no potential thereon and relay K will therefore operate in series with the magnet JHM. No circuit will be completed to operate relay KA however and a busy tone transformer will therefore be connected over the common lead I2 and armatures k3 and Jazz to the lower winding of relay A0 whereupon busy tone will be extended by induction through the windings of relay AO on to the speech conductors. The tone then finds a circuit through condensers QA and QB back to the calling party.

Assuming that an idle line is found however when the operator plugs in and loops the calling junction relay AO operates, the differential relay OC in series therewith not being operated at this stage. At armature aol a circuit is now completed for relay RD by way of rectifier MRB and resistance YB. This relay at armature rd2 prepares an impulsing circuit for relays CJ and C and the selector vertical magnet VM, relay C having already been operated over its left-hand winding by way of armatures b3 and W5 and resistance YC. At armature 1114 a new holding circuit is completed for relay B over its lower winding, the initial operating circuit over its upper winding now being disconnected at the same armature and also the upper winding of relay R. This relay remains operated however since at armature 1116 its lower winding is bridged across the incoming speaking conductors in series with the left-hand Winding of relay DI It will be remembered that when an R. C. X. subscriber originates a call a calling signal is extended to the D. S. R. at the tandem satellite exchange and thence to the main exchange operator while at the same time an idle link 0i!- cuit is caused to associate itself with the calling line. In case all links are engaged however, it is arranged to lock up the calling partys line relay until such time as a link becomes free when the operator will be signalled and the calling line switched through. Should the calling party have hung up during this time, the operator is enabled to ring him and in order that she may be informed on plugging in the condition of the calling line a reverse battery supervision is provided from the R. C. X. Thus if the calling party is on the line, relay DI in the D. S. R. will be operated and will operate relay SY over a circuit extending from earth over armature cl, contacts NR! and armatures 063 and (iii. This relay at its armatures syl and 3 2 reverses the battery potential by way of the windings of relays AC and CC to the main exchange junction so as to give the operator the necessary supervision. In case theoperator on plugging in finds that the calling party has hung up, she may ring him by operating a key at her position which extends an unbalance signal over the junction for example by the connection of earth potential to both the negative and positive conductors, and thereupon operates the differential relay OC in series \mth relay A0. Relay 00 at its armatures ocl and 002 repeats the unbalance signal back over the calling junction so as to bring about the ringing of the calling subscriber at the R. C. X. When the calling party answers, relay DI is operated and in turn operates relay SY to signal the operator accordingly.

The operator now speaks to the calling R. C. X. subscriber to ascertain his requirements, and in order to verify the correctness of the number which he gives as his own, she proceeds to dial back over the connection to set the connecting switch at the calling R. C. X. into engagement with the calling partys line. The first digit of the arid I' in serieswRelay'QE also opens a point calling partys number designates the calling R. C. X. junction in. the tandem satellite exchange, and it is received on relay A in the D. S. R. and serves. to raise the wipers of this switch vertically'to a distinctive level, as shown level L-where a relay OE is operated by way of the vertical bank VB and wiper VW. This relay serves to by-pass the bridge circuit and to provide for the repeating backwardly over the calling R. C. X. junction of further dialled digits. This byepass arrangement is employed in preference to a connection over the wipers of the D- S. R. so that in cases where there may be two or more R. C. X. junctions, the D. S. R. need not perform a hunting operation to connect with the particular junction over which it was taken into use. If it did not connect with the right junction it would be impossible subsequently to connect the calling subscriber locally with a subscriber on his own exchange and yet release the junctions used for the setting up of the connections. 7

Considering now the detailed circuit operation, on the reception of the first train of dial back impulses, relay A0 responds and on the first release a circuit is completed from earth over armatures dcZ3, rcll, aol, (M2 and N22 to operate relay CJ and the-vertical magnet VM and also to hold relay C. The switch wipers are now raised vertically one step whereupon the off-normal springs are mechanically operated and at contacts N2 complete a circuit for relay H over its lower winding from earth, contacts NR3, armature c2, oil-normal contacts C2 and armatures 065 and b4. Relay H at armature k3 short-circuitsthe left-hand winding of relay C so that during the remainder of the impulse train this relay will hold operated due to the combined eifect of its slug and short-circuited winding, the slug on relay CJ enabling this relay to hold likewise. Relay CJat armatures oil and 09'2 disconnects any shunt paths such as the neon tube NT and relay TO from across the impulse circuit to'relay AO so as to prevent interference with the operation of this relay during dialling. Relay RD is also intermittently short-circuited during, the train but remains operated due to the slugging eilect of the short-circuiting. The presence of the metal rectifier MRB in the energising circuit of relay RD prevents the slowing up of the magnet operation which would otherwise result by the direct connection of a comparatively low value non-inductive resistance in parallel with its winding. The resistance of relay RD is moreover such that neither the magnet'VM nor relays CJ and C will hold operated in series therewith.

At the end of thetrain the switch wipers will have been raised vertically to the level corresponding to the digit dialled, say '7, and since this level characterises a call to be routed back to the originating exchange a strapping connection is made from the corresponding contact on the r'ighthand side of the vertical bank V3 to terminal OE, the connection being shown by lines intercepted by circles. Relay AO now remains steadily operated while relays CJ and C release after their slow release periods. 0n the release of relay C a circuit is completed to operate relay OE from earth over armature bl, off-normal contacts N5, armatures WI and 03; vertical bank VB and wiper W to battery via the winding of rel'ay'OE. This relay at armatures Gel and OM by-pass'es the bridge circuit or the D. s. R. and provides an alternative loop across the calling junction c'omprisingthe windings of relays' D in the circuit forrelay C and the vertical magnet VM at armature ce l, and openslthe circuit of relay H at armature 065 so that this relay now releases andpermits the re-operation of relay'C. On the reception of furthertrains of impulses relay A0 responds as before but this time only relay CJ operates and holdsduring each train. At armature c:i3 it short-circuits relays D and I so as to provide an impedance-free impulse re peating loop by way of armature 1102 to the calling exchange for the'duration 'of each impulse train.

After the dialling of the required digits the operator will be connected with the calling subscribers line if the number given by him as his own is correct and the operator now receives a busy indication. As-a further check she is en'- abled to cut-in on thc'engaged line by operating a so-called cut-in key at her position which unbalanced the circuit of relays A0 and OC, and the latter now operates, relay AO remaining "operated during this time over its upper winding. Relay 0C thereupon at its armatures o'cl and 002 repeats this signal. over the junction so that the connecting side of the link in use at the R. C. X. will cut-in on to the engaged line and so enable the operator to ask the number of the. subscriber connected with.

If the numbergiven corresponds to the one which has already been given, the operator now clears down the verification circuit and this is done by extending a high voltage pulse over .the junction which is received in the D.' S. aim relay TOconnected across the speech conductors by Way of a gas discharge tube NT. In response to the high voltage the tube strikes and lowers its resistance suificiently to bring about the operation of relay TO which atarmature tol operates relay RR by way of its lower winding. RelayiRR upon operating, at armature rrl removes the short-circuit from its low resistance upper wind ing over which it now locks in series with relay OE, and at armatures W2 and W3 short-circuits coming junction and a local holding circuit is. completed thereto by way or armatures syi, wt

and W4 and resistance YA. At armature 175 the left-hand winding of relay C which has been. energised due to the removal of the short-circuittherei'rom when relay H restored is now discon-"i nected so that this relay commences. to release. slowly due to its slug. At armaturerrG a cir-- cuit is prepared for the D. S. R. rotary magnet RM in readiness for restoring the switch wipers to normal.

tures 'rrl and b6, rotary magnet interrupter contacts rm, off-normal contacts'NZ, armatures c2 and T16, magnet RM to batteryand the wipers are accordingly rotated to the 1 2th position} where they restore vertically under gravityiand then rotate under'spring control under the banks" On the release of relay C after its slow period, a self-interrupted driving-circuit is completed for the rotary magnet RM from earth? via armature b1, ofi-normal contacts N5. arma-;

back to their full normal position where the magnet driving circuit is opened by the restoring of the off-normal contacts N2 and N5.

When the high voltage pulse is removed relay TO releases, and the similar relays at the calling R. C. X. and at any intermediate tandem R. C. X. are also released. In case the associated switching appartus, in this case the D. S. R., has not by then completely restored to normal relays RR and OE will remain held until the release has been effected. On the restoration to normal of the D. S. R., relays RR and OE are released by the opening of the ofi-normal contacts N5 and these relays on releasing reconnect relay AO across the incoming main exchange junction in readiness to respond to further dialled impulses if any, and disconnect the by-pass circuit between the two junctions. If the call is intended for a subscriber on th same exchange as the originating subscriber, the operator now dials the required number on to relay AO, the first digit of the number resetting the D. S. R. to the same level as before. Relay OE is therefore again operated. and enables the remaining digits of the number to be repeated by means of relay AO back over the calling junction to set the connecting portion of the R. C. X. link circuit into engagement with the required subscriber. It should be mentioned that at the end of the first digit the reverse battery supervision of the calling party is disconnected in the link circuit from. the junction in order to prepare for supervision of the called party. Hence when,

the latter answers after being rung the shunt field relay D in the D. S. R. operates, its righthand polarising winding being energised over the operated armature ii of relay I. Relay D at armature dl operates ,relay DD and this relay in turn at armature dd! brings up'relay SY while at armatures dd2 and dd3 it prepares a circuit for quickly releasing relay RD on the subsequent release of relay AO by removing any short-circuit or holding path. Relay SY at its armatures syl and $112 reverses the battery potential supplied by way of the windings of relays A0 and O0 in series to the main exchange junction so as to indicate to the operator that the called partyhas replied, while she will also hear the commencement of conversation.

The operator now withdraws her plug from the junction jack, whereupon relay AO releases and at armature aol permits relay RD to release quickly. On the release of relay RD the holding circuit of relay B over its lower winding is disconnected at armature rd l and this relay commences to release slowly due to its slug, while at armature 1115 relay K is released. Relay K at armature k5 completes a homing circuit for the junction hunter switch over the following circuit:-earth, homing bank and wiper JHB, armatures I05 and T03, magnet interrupter contacts :ihm, magnet JHM to battery and accordingly the wipers are rotated to the home position I. Armature k6 disconnects the holding circuit of relays KA and JA which thereupon release and the latter at armature 7'a4 disconnects the holding circuit of relay JB. During the release time of this relay the main exchange junction remains guarded by the application of earth over armatures i114 and y'bl to the associated test contact in the junction hunter test bank JI-It. lease of relay Bafter its slow period, the circuit of relay OE is disconnected at armature bl and this relay releases. At armatures b5 and b6 a self-interrupted driving circuit is now completed On the. re-

for the D. S. R. rotary magnet RM over the following circuit: earth which is supplied over common conductor I0 by way of suitable delayed alarm equipment, test link T (used for maintenance routine purposes), armatures c4 and b6, rotary magnet interrupter contacts rm, ofi-normal contacts N2, armatures c2 and b5, magnet RM to battery. Accordingly the switch wipers are rotated to the 12th position whereupon they restore to the normal position in the manner already mentioned. During their restoration relay. IC in the incoming bothway junction equipment is held operated over armature cl and offnormal contacts N l and subsequently releases whereupon the guard earth is removed at armature ici from the test lead P2 thereby marking the R. C. X. junction free for calls to the R. C. X.

If the call has been intended for a subscriber on for instance an R. C. X. adjacent to the tandem satellite exchange, the operator on dialling back over the junction would have set the D. S. R. wipers vertically to a level such as 6 on which are situated junctions to the said R. C. X. In order to initiate rotary hunting over this level it is arranged that on the release of relay C at the end of the vertical motion relay SA is operated over the following circuit: earth, armature bl, offnormal contacts N5, armatures rrl and c3, vertical bank VB and wiper VW, dotted strapping connection between the right-hand vertical bank contact 6 and terminal LS, winding of relay SA to battery. It will be remembered that relay H is operated by way of its lower winding during the vertical motion of the switch and on the release of relay C this initial energising circuit is disconnected but relay H now remains held over the same winding from earth by way of armatures hi and b6 and the rotary magnet interrupter contacts rm. Relay SA at armature safi completes an energising circuit for the rotary magnet RM from earth over armatures hi and 725, contacts rm and N2, armatures c2 and sail,

magnet RM to battery'and the wipers of the D. S. R. are thereupon rotated into engagement with the first set of contacts in the level selected while the magnet interrupter contacts rm are opened. The rotary off-normal springs are mechanically operated on the first rotary step and at contacts NR2 disconnect any further impulsing circuit for relay C and the vertical magnet VM.

A busy junction will be marked by earth potential on the associated P contact, while free junctions are detected by the absence of earth. Spare outlets on the level will be marked as busy by earthing the P contacts concerned.

If the first outlet encountered by the test wiper P is engaged as indicated by the presence of an earth potential, relay H will be held operated over its upper winding and the disconnection of its lower winding by the contacts rm is therefore without effect. The rotary magnet de-energises however, and on the closure of its interrupter contacts the magnet is re-energised to advance the wipers to the second set of contacts in the level selected. This stepping operation continues until a free outlet is reached, or alternatively the wipers are advanced to the 11th position where a busy indication is returned to the operator in a manner to be described.

Immediately the test wiper encounters a free outlet relay H restores quickly and at armature hl disconnects the magnet driving circuit while at armature h2 it applies an earth to the test wiper P to guard the outlet seized. At armature 713 the short-circuit is removed from the left-hand winding of relay C and this relay now re-operates and at armatures c5 and 06 extends the incoming junction by way of condensers Q0 and QD through to the wipers. A seizing loop comprising the windings of relays D and I in series is now extended to the connecting link at the distant R. C. X. so as to prepare it for trains of setting pulses.

In response to further dialling by the operator of the remaining digits of the number, relay AO responds and at armature 1102 repeats the corresponding trains of impulses forward over the wipers of the D. S. R. to set the connecting link at the adjacent R. C. X. and. route the call to its required destination. Relay CJ is operated and held during each train of impulses in the manner already described so as to short-circuit relays D and I during the impulsing.

The calling party is then rung from the connecting link and when he answers the battery feed is reversed over the junction so that the shunt field relay D in the D. S. R.now operates, and operates relays DD and SY in turn. Relay SY upon operating signals the operator who withdraws her plug and releases relays A0 and RD in turn. Relay RD at armature rd5 releases relay K which thereupon initiates the homing of the junction hunter switch and releases relays KA, JA and JB in the manner already described so as to free the main exchange junction. The incoming junction conductor I from the calling R. C. X. is thereupon connected over armatures ogl and oel, condenser QB and armatures ca I, kl, 311.2 and 05 through to the negative D. S. R. wiper while the conductor +l' is connected over armatures og2 and oe2, condenser QA, armatures 0 k2, W3 and 06 to the positive wiper. On the incoming side of condensers QA and QB relay R is bridged across the speech conductors by way of armatures M6 and $115 and the left-hand winding of the shunt field relay DI and the operation of relay R completes a circuit to hold relay B over armatures 11M and 11. On the other side of the condensers relays D and I are connected across the speech conductors and the two' subscribers now converse with each other.

At the conclusion of conversation, when the calling party restores his receiver, relay R releases and releases relay B which initiates the release of the connection.

In case all junctions to the adjacent R. C. X. are engaged, the D. S. R. wipers are rotated to the 11th position where the cam springs are mechanically operated. Thereupon at contacts SI the lower winding of relay A0 is connected to the busy tone transformer so that busy tone is returned both to the operator and to the calling party. Contacts S2 disconnect the upper winding of relay H from the test wiper P so that on the opening of the interrupter contacts rm this relay releases as previously described and opens the magnet driving circuit in order to halt the movement of the wipers. On the subsequent withdrawal of the plug by the operator, relay A0 restores to initiate release of the connection.

As regards relays 0G and JB in the bothway switching equipments BEI' and BE3 respectively, relay OG is operated ona call beingextended from the main exchange through to the R. C. X. Relay JB is operated over the test lead P4 when the associated incoming selector at the tandem satellite exchange is taken into use from the main exchange and at armature yb l serves to guard the associated P contacts in the junction hunter multiple. Both junctions mentioned are operable in a bothway manner depending on the direction of seizure.

Referring now to the local D. S. R. of Figs. 5, 6 and '7, it will be understood that the leads --I, +l, PI and MI connect the switch back to back with a line finder serving local subscribers at the tandem satellite exchange. Leads -2 and +2 connect with a bothway junction to the main exchange and leads 3, +3 and P3 with an ,in-' coming selector at .the tandem satellite exchange, the relays JA and JB again constituting bothway junction equipment such as BE3 in Fig. 1.

Considering now the circuit operation, when a subscriber calls and the line finder locates his line, the loop extended forward over the incoming conductors and.- +I operates relay A and this relay brings up relays B, BA and C in turn. Relay BA at armature bal connects up the dial tone transformer over common lead I3 to, the middle winding of relay A whereupon dial tone is returned to the calling party, while at armature bafi a guard earth is applied to the incoming test lead Pl.

In case the calling party desires to effect connection with another subscriber on the same exchange, he now dials the full number and in response to the first digit, impulses are extended over armature al to the D. S. R. vertical magnet VM so that the wipers are raised to the desired level. During the train relay B remains held due to its slug, while relay CJ is also operated and holds during this time.

On local calls it may be necessary to absorb one or more of the digits dialled and in this instance it is assumed that the first digit of a local number is absorbed. This is effected by providing a strapping from the level on the right-hand side of the vertical bank corresponding to the local digit to the terminal ABS. This results in the operation of relay M on the release of relay CJ at the end of the first impulse train, the circuit being as follows: earth, armatures ba l and oil, vertical bank VB and wiper VW, strapping connection between the contact corresponding to the digit dialled on the right-hand side of the vertical bank VB and terminal ABS, winding of relay M to battery. Relay M locks over its arma-, ture ml and the off-normal contacts N3 to earth via armatures cal, 11'! and ba l and at armature m8 releases relay C. Relay C thereupon completes a self-interrupted driving circuit for the rotary magnet RM from earth, armatures oa3, m6 and 22:12, magnet interrupter contacts rm, off-normal contacts N2, armature 03 to battery via the magnet RM and accordingly the wipers are rotated to the 12th position whence they restore to their normal position.

When thewipers reach the normal position, the off-normal springs are restored and by the opening of contacts N3 the upper winding of relay OA is inserted in series with the winding of relay M so that the latter now holds operated while relay OA operates. Relay CA at armature oal locks over its lower winding, at armature oaZ disconnects the dial tone circuit, at armature oa3 re-operates relay C over its right-hand winding and at armature oa4 prepares a circuit for relay 1-1 over its lower winding in readiness for subsequent rotary hunting for a succeeding local switch on termination of the next dialled digit. At armature 0118 a circuit is completed to operate relay J by way of its lefthand winding in readiness for metering.

On the reception of the train of impulses corresponding to the next digit, rela'y A again re-,

sponds and repeats them to the vertical magnet so as to raise the wipers to a level giving access to the local switches. On the first vertical step contacts N2 complete a circuit including contacts NR2 and armatures c3 and odd to operate relay H and this relay at its armature h2 short-circuits the righthand winding of relay C so that during the impulse train this relay holds by virtue of its short-circuited winding, while relays CJ and B also hold during this time due to their slugs.

At the end of the digit, relays CJ and C release after their slow periods in the usual manner and the latter at armature c3 initiates the rotary hunting operation, the earth being now supplied over operated armatures hi and 17112. When a free outlet to a subsequent local switch is found, relay H releases quickly in the usual manner, disconnects the magnet driving circuit and at armature h2 removes the short-circuiting earth from the right-hand winding of relay C. This relay now re-operates and at armatures c4 and 05 completes a seizing loop including armature a2 and the windings of relays D and I in series over the wipers to the subsequent switch taken into use.

Further digits dialled are repeated by armature 11.2 over the forward loop circuit extending via the wipers, the operated armature 07'4 serving to short circuit the relays D and I during each train. The required local subscriber is therefore connected with over the final selector in wellknown manner and he is then automatically rung. When he replies, battery is reversed back to relays D and I in the D. S. R. so that relay D now operates and at armature dl brings up relay DD.

Relay DD at armature ddE disconnects relay J and during the slow release time of this relay 9. metering pulse is extended back over either the incoming Pl or Ml leads as the case may be in order to operate the calling partys meter. In case fourth wire metering is employed the armatures ddfi and 7'4 serve to apply battery to the MI lead while a strapping connection is made between terminals M and I5 and that between l5 and I6 is omitted. In case positive battery metering over the test wire PI is employed the armatures 7'4 and ddB are connected up by way of a strapping connection between terminals l6 and 15 to armature ball, the connection between terminals I4 and i5 being omitted and the MI lead not being provided. Thus it will be seen that local calls are completed and metered against the calling party in a fully automatic manner.

At the end of the conversation when the calling party replaces his receiver, relay A de-energises and brings about the release in turn of relays B, BA, C, M and 0A. Relays D and DD are released either due to the called party hanging up or to the opening of the forward loop at armature a2. The D. S. R. is restored to normal in the manner previously described when relay C releases. The incoming test conductor PI is guarded in the usual manner over contacts NI and armature cl until the switch is fully restored.

In case all the local switches are engaged, the D. S. R. wipers are rotated to the 11th position where relay H is released at contacts S2 to disconnect the driving circuit while busy tone is returned to the calling party over common lead l2 and contacts SI.

If for any reason the incoming leads to the switch are looped and the call is not proceeded with, for example due to a faulty line or as a result of the subscriber accidentally leaving his receiver off the hook, it is arranged that the D. S. R. is automatically released after a suitable period as measured by common timing equipment and the calling partys line equipment is then looked up to prevent ftu'ther seizure of switches until the fault is cleared.

When the D. S. R. is taken into use, the lefthand winding of relay TP is connected over armatures ML 1229, tclfi and 02 to common lead S. The common leads S and Z extend to motordriven cams arranged to supply earth pulses bearing a definite time relation. When the timing mechanism is in its normal position earth is applied to the S lead so that if the switch is taken into use some time during rotation of the cams earth will not be applied to the S lead until the mechanism returns to the normal position. When this occurs relay TP operates over its left-hand winding andthereupon locks over its right-hand winding. At armature tpt earth is connected to the common start lead ST to cause the timing mechanism to perform another revolution while at armature tpZ relay B is connected to the common lead Z. After the lapse of the predetermined period, earth is applied to the Z lead and if the subscriber has failed to dial by this time, in which case relay I? will still be operated, the earth will be extended over armature tpll to short-circuit relay B and cause its release. Relay B releases relays BA and C in turn and also relays M, GA and J if the absorbed digit has already been dialled and during the release of relay C the guard earth is removed from the incoming test lead Pl so as to bring about the immediate release of the line finder and the locking up of the calling partys line equipment. Relay A will have been released on release of the line finder and hence on the release of relay C the D. S. R. will now be available for further common use.

The forced release arrangement described will also come into operation if at the end of the conversation on a call not involving the manual board i. e. a call during which relay M is operated, the calling party should fail to hang up although the called party has done so. Under this condition relay TP will be connected up to the S lead I over armatures ddl, m9, 7'5 and 02. The switch will be restored to normal in the usual way on the release of relay C.

In case the call is intended for a subscriber external to the tandem satellite exchange, the calling subscriber dials a distinctive digit which raises the D. S. R. wipers to a level on which relay TD is operatedrby Way of the vertical bank and wiper and strapping connection between the righthand vertical bank contact corresponding to the digit dialled and terminal MB. Relay TD upon operating at armature td5 operates relay RC and at armature id! disconnects the dial tone circuit. Relay RC at its armature re! and T02 initiates the hunting of the junction hunter switch to select a junction to the main exchange and when this is found, relay K is operated in the manner previously described and at armature k3 applies guard earth to the junction hunter test Wiper J 4 whereupon relay J A in the bothway equipment is operated and subsequently relay JB. Relay K opens the circuit of relay RC and during the release time of this relay a short pulse of ringing is extended from common lead H and armatures k6 and M3 to the negative junction lead 2 so as to bring the operator into the circuit. On the release of relay RC relays A0 and 0C are connected to the main exchange junction so that when the operator plugs in relay AO operates.

Relay AO operates relay RD by way of rectifier MRB and resistance YD to battery and this relay thereupon at its armature rd3 disconnects the righthand energising winding of relay Cwhich ing of relay 0A, armature tdi to battery via a protective resistance. Relay RDalso at armature 'rdZ transfers the vertical magnet impulsing circuit to the control of relay A0. Relay 0A in addition to bringing about other circuit changes, at armature oaS operates relay SY which thereupon at armatures SU! and 51 2 reverses the battery extended on to the main exchange junction by way or" the windings of relays A0 and 00 so as to provide a supervision to the operator that the D. S. R has restored to normal. Hence aft-er speaking to the calling party and ascertaining his requirements she may at once set up a verification connection.

For verification purposes the operator now dials the number of'the calling party and theimpulses operate relay A0 which brings about the raising of the D. S. R wipers to a distinctive local level on which a strapping connection is made between the corresponding contact on the righthand side of the vertical bank and terminal LOC. Hence at the end of the first digit relay M is operated over armature r115. Relay H is operated over its lower winding in the usual manner on the first vertical step since relay 0A is 0-perated and consequently on the release of relay C at the end of the train a self-driving circuit will be completed for the rotary magnet. When a free outlet to a succeeding local switch is found, relay H releases and re-operates relay C so as to extend a seizing loop comprising the windings of relays D and I in series and the operated armature (102 over the wipers of the D. S. R. to the switch taken into use. Further digits dialled by the operator are repeated by this armature 0.02 so as to set up the local train of switches and thus obtain connection with the calling subscriber. If the operator encounters a busy indication, as'should be the case if the correct number has been given, she may cut-in on the engaged line by unbalancing the junction line to bring up relay OC which at its armatures cal and 002 relays the unbalance signal to the final selector to cause it to cut-in.

Having identified the calling subscriber, the operator now extends a pulse of high voltage over the junction to release the verification connection and this is received on relay TO which is bridged across the loop in series with the gas discharge tube NT and which upon operating energises relay RR. Relay RR breaks the loop forward over the D. S. R. wipers at its armature 1'15 so as to release the local train of switches and also at armature TTl locks over its upper winding in series with relay M and opens the locking circuit of relay 0A so that this. relay is now dependent on the operated armature toZ- Hence at the completion of the high voltage pulse when relay TO releases, the relay 0A also restores and releases relay C which completes the D. S. Rcrelease circuit so that the wipers are again restored to normal. When this occurs the opening of the off-normal contacts N3 allows relays RR and M Since relay TD is still held operated to release.

from earth over armatures D114 and 1111, relay 0A will now operate again over its upper winding and re-operate relay C in readiness for a further vertical movement.

If the call is to be completed via an R. C. X. accessible from the tandem satellite exchange, the operator now dials back over the junction so level carrying junctions to the required adjacent R. C. X. The corresponding level of the vertical bank is again connected to terminal LOC so that on the release of relay CJ at the end of-the train of impulses, relay M is operated and locks over its armature ml in series with the upper windings of relay 0A. Relay H is also operated at the beginning of the vertical movement and on the release of relay C at the end of the digit the switch hunts for a free junction extending in the desired direction in the usual manner. Further impulses are now repeated by armature (1.02 over the junction to set up the desired connection.

The wanted party is now rung and when he answers battery is reversed over the junction to operate relay D which in turn operates relay DD and this relay brings about the operation of re' lay SY so as to signal to the operator'that' the called party has replied. The operator now dockets the call against the calling party, since metering is not automatically effected under these conditions, and removes her plug from the junction jack.- Relay A0 now releases and re releases relays RD, TD and K in turn so asto free the main exchange junction for further use,

the two subscribers being linked together by way of the D. S. R. f

If the call is intended for a subscriber on an exchange accessible from the main exchange, the operator after setting up and releasing the verification connection takes up the other plug of her cord circuit which she plugs into a jack connecting to a junction leading in the required direction.

On all calls described it will be noted that the release of the D. S. R. is under control of the calling party, relay A in releasing initiating the release of the D. S. R. at its armature al by releasing relays B, BA and C in turn and opening as to set the D. S. R to a particular local routing the loop forward at armature a2. In the case of a main exchange call the armature a2 also breaks the battery feed normally extended via relay A0 to the main exchange junction so as to give a clearing signal to the mainexchange. The junction hunter in this case is also restored to the home position on release of relays TD and K in turn following that of relay BA.

In case on a call to the manual board all main exchange junctions are engaged, the junction hunter wipers are rotated to the last position where relay K is operated in the manner described in connection with the switch of Figs. 2-4 and operates relay J to return a busy indication to the calling party.

Contacts on the right-hand side of the vertical bank which correspond to spare code digits are cross-connectedto terminal SC so that in the event of such digits being dialled relay J will be operated to returna busy tone.

We claim:

1. In a telephone system, a main exchange, a tandem exchange, junction lines interconnecting said exchanges, a discriminating selector repeater unit in the tandem exchange including a hunting switch and a numerical switch, local switches in the tandem exchange, exchanges adjacent said tandem exchange, means in said unit responsive to the receipt of a call for operating said hunting switch to select an idle junction line extending to the main exchange, and means in the main exchange for transmitting impulses back over the selected junction line to operate said numerical switch to extend the connection to said local switches or said adjacent exchanges.

2. In a telephone system, a main exchange. a local exchange, junction lines interconnecting said main and local exchanges, a discriminating selector repeater unit including an individual hunting switch and an individual numerical switch in the local exchange, local switches in the local exchange, an exchange adjacent said local exchange having access to said unit and accessible from the banks of said numerical switch,

means in said unit responsive to the receipt of a call from one of said adjacent exchanges for operating said hunting switch to select an idle one of said junction lines extending to the main exchange, means in the main exchange for transmitting impulses back over the selected junction line to said unit, means in said unit for repeating said impulses, and wipers in said numerical switch operated in response to the first digit of said repeated impulses for extending the connection to one of said local switches to establish a path for transmission of the succeeding digits of said repeated impulses.

3. In a telephone system, a main exchange, a tandem exchange, junction lines interconnecting said exchanges, a discriminating selector repeater unit in the tandem. exchange including a hunting switch and a numerical switch, means including a two-conductor trunk line for seizing said unit in response to the initiation of a call over said trunk line, means in said unit responsive to said seizure for operating said hunting switch to select an idle junction line extending to the main exchange, means in the main exchange for transmitting series of impulses back over the selected junction line to said unit, means in said unit responsive to the first of said series of transmitted impulses for operating said numerical switch to extend the connection back to said two conductors of said trunk line, and means in said unit for repeating the remaining series of 7 impulses back over said two conductors of said trunk line to complete the desired connection in accordance with the repeated impulses.

4. In a telephone system, a main exchange having an operators position, a local exchange, junction lines interconnecting said exchanges and terminating in said position, a discriminating selector repeater unit in the local exchange, local subscribers lines terminating in the local exchange; local switches in the local exchange for extending connections to said local lines, exchanges adjacent said local exchange, a numerical switch included in said unit having access to said local switches and to said adjacent exchanges, a hunting switch included in said unit having access to said junction lines, means whereby said numerical switch is operated by a calling one of said local lines to extend a connection from the calling line to said local switches in case the calling party desires a connection to a local called line, and means whereby said hunting switch is operated to select an idle one of said junction lines to said position and said numerical switch is operated over the selected junction line by the operator at said position to extend a connection from the calling line to one of said adjacent exchanges in case the calling party desires a connection including said adjacent exchange.

5. In a telephone system, a first exchange, a second exchange having an operators position,

a third exchange, a discriminating selector repeater in the first exchange, a calling line in the tandem exchange, a main exchange having an operators position, a discriminating selector repeater in the tandem exchange, a junction line extending from the first exchange to said selector repeater in the tandem. exchange, means responsive to a call in the first exchange for seizing said selector repeater over said junction line, means responsive to said seizure for extending the call through the tandem exchange to said operator's position in the main exchange, means for transmitting series of digit pulses from said operators position to said selector repeater, means in said selector repeater operated in response to the receipt of the first of said transmitted digits, and circuits completed by said last means for repeating the succeeding transmitted digits back over said junction line to said first exchange.

7. In a telephone system as claimed in claim 1 including means for immediately releasing the numerical switch of said selector repeater unit after its operation in case the impulses transmitted over said junction line comprisea digit of a predetermined value.

8. In a telephone system as claimed in claim 5 including means in said selector repeater for transferring the control of said connection to said calling line in response to operator withdrawing after completion of the desired connection.

9. In a telephone system as claimed in claim 3 including circuits in said unit for repeating impulses back over said two-conductor trunk line, said circuits being prepared in response to said operation of said numerical switch by the first series of impulses transmitted from the main exchange.

10. In a telephone system as claimed in claim 4 including means whereby said hunting switch is operated to select an idle junction line to the operators position only in case said numerical switch is operated in response to the receipt of a predetermined train of impulses from the calling line.

11. In a telephone system as claimed in claim. 4 including means whereby said hunting switch is operated to select an idle junction line to the operators position only in case said numerical switch is operated in response to the receipt of a predetermined train of impulses from the calling line, and means for restoring said numerical switch to its normal position in response to the operator replying.

12. In a telephone system as claimed in claim 4 including means for transmitting digits from the calling line to control said operation of said numerical switch and said hunting switch to establish said desired local connection or said connection to an adjacent exchange dependent upon the value of the first transmitted digit.

13. In a telephone system at claimed in claim 2 including means at the main exchange for transmitting a signal comprising a high voltage pulse over said selected junction line to said unit, and means in said unit responsive to receipt of said signal for restoring said numerical switch to normal.

14. In a telephone system as claimed in claim 3 including means at the main exchange for trans mitting a signal comprising a high voltage pulse over said selected junction line to said unit, and means in said unit responsive to receipt of said signal for restoring said numerical switch to normal and for connecting said signal to said two conductors of said trunk line over which said unit was seized.

15. In a telephone system as claimed in claim 3 including a timing device efiective after a predetermined time to release the connection in case no impulse transmission takes place and in case the calling party delays to hang up after the called party has done so.

16. In a telephone system as claimed in claim 6 wherein said selector repeater in response to said first digit is operated to a position characteristic of said first exchange before said circuits are effective to enable the operator to dial back over said junction line to said first exchange.

17. In a telephone system as claimed in claim 6 including means for giving the operator a signal to indicate whether the party originating the call is still on the line when said call is extended to said operators position.

18. In a telephone system as claimed in claim 6 including means effective after the connection has been set up to the operator for reoperating said selector repeater toestablish a verification connection to the party originating the call.

19. In a telephone system, a main exchange, a tandem exchange, junction lines interconnecting said exchanges, a discriminating selector repeater unit in the tandem exchange including a hunting switch and a numerical switch, local switches in the tandem exchange, exchanges adjacent said tandem exchange, means including a two conductor trunk line for seizing said unit in response to a. call from one of said adjacent exchanges,

means in said unit responsive to said seizure for operating said hunting switch to select an idle junction line extending to the main exchange, means in the main exchange for transmitting series of impulses back over the selected junction line to said unit, means in said unit responsive to the first of said series of transmitted impulses for operating said numerical switch to extend the connection to said local switches or to said conductors of said trunk line dependent upon the number of impulses in said first series, and means in said unit *for repeating the remaining series of impulses to said local switches or back over said two conductors of said trunk line dependent upon the extension completed in response to said first series of impulses.

20. In a telephone system, a main exchange having an operators position, a local exchange, junction lines interconnecting said exchanges and terminating in said position, a discriminating selector repeater unit including a hunting switch and a numerical switch in the local exchange, local switches in the local exchange, exchanges adjacent said local exchange, local subscribers lines terminating in the local exchange, means responsive to the initiation of a call by a local subscriber for seizing said unit, means controlled by the calling subscriber for operating said numerical switch and said local switches to complete a connection to a local called subscribers line; means controlled by the calling subscriber, in case an external connection to an adjacent exchange is desired, for operating said numerical switch to a distinctive position; means for automatically operating said hunting switch to select an idle junction line to said operators position in response to said operation of said numerical switch to said distinctive position, and means controlled by the operator for releasing and reoperating said numerical switch to extend the connection to the desired adjacent exchange.

CHARLES EDMUND BEALE. IDRIS TREVOR RICHARDS. OWEN AVIS PEARCE. 

